The debate between sedation and anaesthesia for children undergoing MRI.
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Biomedical subjects
Publications and source records attributed to M R Sury.
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BACKGROUND: Children generally lie still enough for magnetic resonance imaging (MRI) only if they are asleep, either under sedation, which is deeper than conscious sedation, or under anaesthesia. Anaesthesia resources, however, are limited, and non-anaesthetists must use sedation frequently. Demand for MRI has increased and the failure of our sedation regimen led to an impractical demand for anaesthesia and unacceptable waiting times for scanning. We have therefore developed a nurse-led sedation service in a designated unit next to the scanner. This study assessed the safety and efficacy of this approach. METHODS: Children who required MRI were sedated in the unit by designated sedationist nurses, who used an oral drug regimen (according to weight and age from conception: weight <5 kg, 50 mg/kg chloral hydrate; 5-10 kg, 100 mg/kg chloral hydrate; 10-20 kg, 1 mg/kg temazepam plus 0.25 mg/kg droperidol; >20 kg temazepam and droperidol as directed by radiologist, maximum doses 20 mg and 5 mg respectively). Nurses checked patients for their suitability, charted and administered the drugs according to a protocol, and monitored the children throughout the sedation. We prospectively audited failure and complications of sedation. FINDINGS: During the 30 month study, there were 1155 sedations. 61 (5%) were unsuccessful, and there were no adverse events relating to the airway or breathing. After scanning had finished all children, in response to gently pinching the nose, could open their mouths to maintain their airway. INTERPRETATION: This study suggests that it is possible to have a nurse-led sedation service for MRI of children that is both successful and safe.
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Sevoflurane has a lower blood-gas solubility and a less pungent odour than halothane; this may allow more rapid induction of anaesthesia. In a randomized, blinded study, we compared the induction characteristics of maximum initial inspired concentration of 8% sevoflurane and 5% halothane using conventional vaporizers in children aged 3 months to 3 years. There was no statistically significant difference in induction times between the two groups: mean times to loss of consciousness were 1 min 12 s (SD 18 s, range 40 s-1 min 44 s) for sevoflurane and 1 min 16 s (SD 17 s, range 50 s-1 min 52 s) for halothane, although these times were shorter than in previous studies using a gradual increase in vapour concentration. A small number of complications were noted in both groups, although none interfered with induction of anaesthesia. Struggling scores were lower in the sevoflurane group than in the halothane group (chi-square for trends = 6.34, P < 0.02). A significant number (11 of 15) of parents of children in the sevoflurane group who had previous experience of halothane induction preferred sevoflurane (chi-square for trends = 4.03, P < 0.05). We conclude that with this technique, induction was rapid with both sevoflurane and halothane. Our assessment of patient struggling and parents' perceptions suggests that induction with sevoflurane was more pleasant than with halothane.
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The induction characteristics of sevoflurane and halothane were compared in 81 children aged 6 months to 6 years. The mean time taken to achieve loss of eyelash reflex was significantly shorter with sevoflurane than with halothane (sevoflurane, mean time (SD) 1 min 41 s (35 s), halothane, mean time (SD) 2 min 17 s (43 s), t = 4.11, p = < 0.01). The mean time taken to complete induction (to achieve steady spontaneous ventilation and small pupils with central gaze) was also shorter in children induced with sevoflurane (sevoflurane, mean time (SD) 3 min 58 s (1 min 8 s), halothane, mean time (SD) 4 min 50 s, (1 min 27 s), t = 2.29, p = 0.027). Effects on heart rate, blood pressure and oxygen saturation during induction were similar for both agents. There were no major complications during induction with either halothane or sevoflurane.
The recovery characteristics of sevoflurane and halothane anaesthesia were compared in 40 children aged 6 months to 6 years undergoing day case surgery. The mean time taken to open eyes after surgery had ended was appreciably and significantly shorter after sevoflurane than after halothane (sevoflurane, mean time (SD) 7 min 52 s (5 min 46 s), halothane, mean time (SD) 15 min 50 s (9 min 2 s), t = 3.32, p = 0.002). The time taken to be ready for discharge from the recovery unit to the ward was also significantly shorter after sevoflurane than after halothane (sevoflurane, mean time (SD) 12 min 46 s (4 min 11 s), halothane, mean time (SD) 19 min 13 s (9 min 48 s), t = 2.7, p < 0.01). However, more children were in pain and given analgesia after sevoflurane (p < 0.01) and the mean time to reach the criteria for discharge home was similar in both groups (sevoflurane, mean time (SD) 2 h 9 min (17 min), halothane, mean time (SD) 2 h 4 min (8 min)). There were no major complications in either group.
In a randomized blinded study we compared two colloid solutions in 30 neonates undergoing major surgery. Fifteen neonates received 4.5% Human albumin solution (HAS) (mean volume 25.6 ml.kg-1, SD 9.5) and the others received Haemaccel (Hoechst) (24.9 ml.kg-1, SD 10). Pre and postoperative plasma albumin and haemoglobin concentrations and plasma colloid osmotic pressure (COP) were compared. In the group given Haemaccel there was an appreciable and statistically significant decrease in the mean plasma albumin concentration from 34.27 to 28.27 g.1(-1) (mean difference 6, CI 3.38 to 8.62) and the mean COP decreased significantly from 22.2 to 19.9 mmHg (mean difference 2.3, CI 0.3 to 4.5). In the HAS group there was no significant change in either the plasma albumin concentration or COP. There was a small but significant decrease in the mean haemoglobin concentration from 15.92 to 14.35 g.dl-1 (mean difference 1.56, CI 0.57 to 2.55) after HAS. We conclude that HAS is the superior colloid for volume replacement in neonates undergoing surgery.
Spontaneous neonatal gastric perforation is a rare neonatal event. We report three cases which demonstrate that significant cardiovascular instability can occur in these patients. We suggest that if the diagnosis is known preoperatively, invasive monitoring should be instituted, and that it is likely that these children will require large volumes of colloid and inotropic support.
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We have assessed the effect of lengthening the expiratory limb of an Ayre's T-piece from 0.5 to 10 m for ventilation with a Nuffield series 200 ventilator and Newton valve, as this equipment is potentially suitable for infants and young children during anaesthesia for magnetic resonance imaging (MRI). We used lung models with compliances and resistances representative of the respiratory system with intubated trachea of a neonate, infant and child weighing 15-20 kg. The effects on ventilation were small, being greatest with the largest lung model where the longer T-piece resulted in a reduction in tidal volume from 261 to 236 ml and an increase in intrinsic and extrinsic positive end-expiratory pressure from 0.20 to 0.32 kPa and from 0.14 to 0.25 kPa, respectively. Such changes are unlikely to be clinically important and can be obviated by using the ventilator with the standard valve in children weighing 15-20 kg.
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A series of 20 infants undergoing general anaesthesia for pyloromyotomy were studied in a randomised, blind and controlled trial to determine the postoperative behavioural and cardiorespiratory effects of wound infiltration of bupivacaine. Ten infants received bupivacaine (0.6 ml/kg, 0.25% = 1.5 mg/kg) injected intradermally into the wound during general anaesthesia and 10 infants received general anaesthesia only. Postoperatively, an independent observer assessed conscious level, crying, posture and facial expression using a simple numerical scoring system, and also recorded heart and respiratory rates over a 2-h period. Infants who had received bupivacaine were observed to have higher respiratory rates and behaviour scores, although these differences were not statistically significant. These results indicate that wound infiltration with bupivacaine offers no obvious advantage to infants following pyloromyotomy.
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